One control device of a hybrid vehicle is disclosed in patent document 1 (JP-A-2010-241190). This control device predicts a warming-up time of an engine and a charging time of a battery at the time of cold-starting the engine and extracts a set of operating points in which an engine warming-up completion timing and a battery charging completion timing are included within a given range and performs a load operation at any one of the operating points of the extracted set.
The conditions of cold-starting the engine are not constant but are variously changed. For example, only by adding a load of generating electricity to a load of cold-starting the engine, the charging of the battery is completed before the warming-up of the engine is completed or the warming-up of the engine is completed before the charging of the battery is completed.
Regarding this, according to the control device of the hybrid vehicle disclosed in the patent document 1 (JP-A-2010-241190), the warming-up of the engine and the charging of the battery are surely completed within a given range. Hence, this can eliminate a continuous idling operation of no load and a continuous release of thermal energy by the load operation. As a result, at the time of cold-starting the engine, by decreasing a difference between the engine warming-up completion timing and the battery charging completion timing, it is possible to reduce fuel consumption at a low efficiency and hence to improve a fuel economy.
By the way, in a hybrid vehicle using an engine and a motor generator as a driving source for driving the vehicle, the engine is intermittently driven under a low-load driving condition, so when heating using the coolant of the engine as a heat source is performed, a coolant temperature is low and an amount of heat for the heating is short. For this reason, in a case where the heating is performed under the low-load driving condition, generally, the engine is operated to increase the coolant temperature and further an electric heating system is operated to make up for the shortage of the amount of heat for the heating.
However, in the related art, an amount of heat for the heating that is supplied by the heating using the coolant of the engine as a heat source and an amount of heat for the heating that is supplied from the electric heating system are not controlled in consideration of a change in the coolant temperature and a change in the state of charge of a battery at the time of operating the heating.
For this reason, when the electric heating system is continuously used as a heat source, the coolant temperature is sufficiently increased but the state of charge of the battery is reduced (heat is adequate and electricity is short), or when the coolant temperature is comparatively low and the coolant of the engine is continuously used as the heat source, the state of charge of the battery is within an adequate range but the coolant temperature becomes lower (heat is short and electricity is adequate).
In this way, in a case where a balance between the coolant temperature and the state of charge of the battery becomes bad, in order to bring both of the coolant temperature and the state of charge of the battery into target ranges, it can be thought to select an engine operating point at which a heat generation ratio is large in the operation control of the engine, or as shown in patent document 1 (JP-A-2010-241190), to select an engine operating point in an engine operating region in which an engine coolant temperature at which a warming-up operation is completed and the state of charge of the battery at which a charging operation is completed are reached at the same time. However, when the engine operating point like this is selected, a fuel consumption will be increased.
Here, in the patent document 1 (JP-A-2010-241190), an engine operating region is extracted in which the engine coolant temperature at which the warming-up operation is completed and the state of charge of the battery at which the charging operation is completed are reached at the same time and an engine operating point at which the fuel consumption becomes minimal is selected in the engine operating region. However, in the first place, the extracted engine operating region is greatly separate from operating points selected from a viewpoint of minimizing the fuel consumption among all possible engine operating points, so that as compared with these operating points, the engine operating points selected as in the patent document 1 (JP-A-2010-241190) are increased in the fuel consumption.